As business transactions of this type, there are conventionally, for example, transactions of stocks and bonds by telephone in stockbrokers, transactions by telephone of goods sold through television, radio, books, and so on, reservation transactions to lodging facilities and transport facilities by telephone, and so on. Since these are all the ordering by voice through telephone, voice recording systems are used for keeping the ordering records.
However, these voice recording systems each use a system internal timepiece or the like and, therefore, even if a voice recording time is altered on the recording side, it is not possible to prove the alteration of the voice recording time and thus the system is advantageous to the recording side.
In view of this, as a voice recording system of this type, there has been proposed offering of a service that improves reliability of a time of a business transaction such as ordering by voice, by recording the content of speech in a third-party service facility or issuing a digital certificate accompanied by time information (e.g. Japanese Unexamined Patent Application Publication (JP-A) No. 2004-172694 or Japanese Unexamined Patent Application Publication (JP-A) No. 2004-194306).
However, the foregoing conventional voice recording systems have a problem that even if a system user such as a stockbroker has altered conversation voice data before time authentication, it cannot be detected. Accordingly, the conventional voice recording systems have a problem that it is not possible to prove that no conversation voice is present before a certain time.